This invention belongs to the broad realm of fiber optics and pertains more specifically to a laser module comprised of a serial arrangement of a laser assembly, an optical isolator assembly and an optical fiber assembly. The invention also specifically concerns a method of adjusting the angular position of the optical isolator assembly with respect to the laser assembly for optimum forward loss and isolation characteristics.
Optical transmission systems have been known which employ optical fibers in combination with such sources of coherent beams of light as semiconductor lasers and light-emitting diodes. Constituting indispensable parts of such optical transmission systems are what are known to the specialists as photosemiconductor modules. The photosemiconductor module serves to mechanically interconnect the light source and one end of a length of optical fiber. Also, comprising a converging lens system, the photosemiconductor module functions to direct the beam of light from the source into the optical fiber.
In the use of a semiconductor laser as the light source, its operation would become unstable should it be exposed to reflections of the beam as from the end of the optical fiber. Therefore, in such cases, a semiconductor laser module is adopted which incorporates an optical isolator (shown in FIG. 1 of the drawings attached hereto) between a semiconductor laser assembly and an optical fiber assembly. Operating on the principle of Faraday rotation, the optical isolator transmits the light from the laser assembly toward the fiber assembly with much less loss than in the opposite direction.
As incorporated in a semiconductor laser module, the Faraday rotation isolator now under consideration has its optical axis offset from that of the laser assembly. The angular position of the isolator about its optical axis is in need of adjustment relative to that of the semiconductor laser assembly for optimum performance. As conventionally practiced, however, the adjustment of the angular position of the isolator has often given rise to undesired variations in the forward loss and isolation characteristics of the isolator with the possible deformations of the module components or with a change in the output wavelength of the semiconductor laser in use. Such inconveniences heretofore encountered in the art will be later described in more detail with reference to the accompanying drawings.